Synthesis of cadmium sulfide using the laser-induced reaction of dialkylcadmium and organosulfur compounds

ABSTRACT

Cadmium sulfide is formed successfully from the laser-induced chemical  reion between a first reactant of a dialkylcadmium and a second reactant of a dialkylsulfide. Infrared laser radiation in the range of 10.4 or 9.4 micrometers is provided by a continuous-wave CO 2  laser. In single line operation, output powers between 10 and 150 watts/centimeters square (W/cm 2 ) are obtained by variation of the CO 2  -N 2  -He gas mixture in the laser. The process procedure and sample handling is accomplished using standard vacuum line techniques. The irradiation of dimethylsulfide at R(18) of (00°1-10°0) for 5 seconds at 100 W/cm 2  produced the products methane, ethane, and sulfur. A mixture of a dialkylsulfide (CH 3 ) 2  S, and a dialkylcadmium (CH 3 ) 2  Cd is irradiated at R(18) of (00°1-10°0), 979 cm -1  for a total of 5 seconds at 100 W/cm 2  to form CdS on the windows of the reaction cell. A higher yield of CdS is obtained when the sensitizer SR 6  is added to the mixture of the reactants. Excitation of the mixture occurs using P(20) of (00°1-10° 0) at 944 cm -1  for 5 seconds at 100 W/cm 2 . The representative torr pressures of the reactants are for (CH 3 ) 2  Cd 33 torr combined with (CH 3 ) 2  S to total 100 torr pressure prior to irradiation. The efficiency when SF 6  (6 torr) plus (CH 3 ) 2  Cd (22.4 torr) is combined with 54.5 torr of (CH 3 ) 2  S and irradiated is improved.

DEDICATORY CLAUSE

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION

Cadmium sulfide single crystal is used as a UV detector and in combination with other materials indium antimony (InSb) as a detector for UV and IR detectors. The final product material must meet a very strict set of specifications with respect to spectral transmission, mobility, resistivity, and detector lifetime. The single crystals are prepared using a "proprietary" process which involves chemical vapor deposition by Eagle Picher Laboratories, who is at present the single supplier. It is concluded that the characteristics of the single crystal are drastically affected by the purity of the cadmium sulfide powder used as a precursor to the single crystal. The basis for this conclusion is supported by P. D. Fochs et al, Report No. AE-1-G.1453, Clevite Corporation, Report No. FTD-TT-65-555, General Electric Company, Report No. SR-2,65gc-03 136, and Bell and Howell Research center, Technical Report AF 33-615-276.

Because of the high priority and importance of high purity of precursor material for a single crystal product, a variety of studies have been conducted over the past twenty years with the objective of perfecting a process which would produce purer starting material for ultimate growth of single crystals with specific properties. Predominant leaders in this area include Eagle Picher Laboratories and the Clevite Corporation Research Laboratory. The synthetic work for cadmium sulfide performed by these companies involved the chemical reaction of the elements with thermal activation as necessary.

Hydrogen sulfide is known to be acidic in solution; however, a reaction in liquid solution to yield cadmium sulfide is not desired to be pursued since the required level of purity of the finished product by this route cannot be achieved.

A laser-induced chemical reaction to yield high purity cadmium sulfide is worthy of consideration and further investigation; therefore, an object of this invention is to provide a laser-induced reaction to precisely produce sulfur to react with cadmium from an organocadmium compound selected from a dialkylcadmium compound to yield a high purity thermodynamically stable cadmium sulfide.

A further object of this invention is to provide a laser-induced chemical reaction between a dialkylsulfide and a dialkylcadmium compound to yield high purity thermodynamically stable cadmium sulfide.

Still, a further object of this invention is to provide a laser-induced chemical reaction wherein the compound SF₆ is mixed with a dialkylsulfide compound and a dialkylcadmium compound wherein the compound SF₆ has a fundamental which allows the excitation to occur by absorption of laser energy followed by collisional transfer to effect a higher yield of high purity thermodynamically stable cadmium sulfide.

SUMMARY OF THE INVENTION

A method of synthesis comprises a laser-induced chemical reaction between a first reactant of a dialkylcadmium and a second reactant of a dialkylsulfide to form high purity cadmium sulfide. The reactants are induced to react by laser irradiation wherein the reaction is carried out in a stainless steel cell (5×10 cm) equipped with O-ring seals for securing windows (5 cm diameter) onto the cells. Potassium chloride windows are used on the short pathlength (5 cm) for recording the infrared spectra. A zirconium selenium (ZrSe) window is used to transmit the incident infrared radiation; however, since only about 65% of the incident radiation is transmitted through the ZrSe window the laser power available to the sample must be adjusted accordingly.

Infrared laser radiation in the range of 10.4 or 9.4 micrometers is provided by a Coherent Radiation Laboratories model 41 continuous-wave CO₂ laser. In single line operation, output powers between 10 and 150 W/cm² are obtained by variation of the CO₂ -N₂ -He gas mixture in the laser.

Dimethylsulfide is irradiated at R(18) of (00°1-10°0) for 5 seconds at 100 W/cm². The products formed are methane, ethane, and sulfur.

A mixture of a dialkylsulfide, (CH₃)₂ S, and a dialkylcadmium, (CH₃)₂ Cd is irradiated at R(18) of (00°1-10°0), 979 cm⁻¹ for a total of 5 seconds at 100 W/cm². CdS is formed on the windows and methane and ethane are other products that remain in the gaseous mixture. A higher yield of CdS is obtained when SF₆ is added to the mixture of the reactants. Excitation of the SF₆, (CH₃)₂ S, and (CH₃)₂ Cd mixture occurs using P(20) of (00°1-10°0) at 944 cm⁻¹ for 5 seconds at 100 W/cm². Using SF₆ results in an enhanced reaction of (CH₃)₂ S and (CH₃)₂ Cd to produce a higher yield of high purity CdS.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a typical experimental setup for laser-induced chemical reaction and monitoring the induced reaction.

FIG. 2 depicts infrared spectra curves A, B, and C which respectively represent (CH₃)₂ Cd at 33 torr, (CH₃)₂ Cd and (CH₃)₂ S mixed to form a mixture at 100 torr, and the mixture of (CH₃)₂ Cd and (CH₃)₂ S after irradiation.

FIG. 3 depicts infrared spectra curves A, B, and C representing the result of the laser-induced reaction of (CH₃)₂ S and (CH₃)₂ Cd as enhanced with the sensitizer SF₆.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preparation of cadmium sulfide powder using laser photochemistry is achieved by employing the typical setup depicted in FIG. 1 of the drawing.

An organosulfur compound is used as a reactant to precisely produce sulfur which reacts with cadmium released from another reactant, a dialkylcadmium, to produce high purity cadmium sulfide.

Sample handling is accomplished using standard vacuum line techniques. The reactants are gaseous products, and the gas phase reaction which is induced by infrared laser radiation is carried out in stainless steel cells (5×10 cm) equipped with O-ring seals for securing windows (5 cm diameter) onto the cells. Potassium chloride windows are used on the short pathlength (5 cm) for recording the infrared spectra. A zirconium selenium (ZrSe) window is used to transmit the incident infrared radiation; however, since only about 64% of the incident radiation is transmitted through the ZrSe window the laser power available to the sample must be adjusted accordingly.

Infrared spectra are recorded on a Mattson Sirius 100 interferometer equipped with a water-cooled carborundum source, iris aperture, potassium bromide (KBr) beamsplitter, and triglycine sulfate (TGS) detector. Interferograms are transformed after applying a triangular apodization function with an effective spectral resolution of 1.0 cm⁻¹. This resolution is sufficient to allow unequivocal identification of all the products as well as to monitor the decrease of the starting material from its infrared absorption bands.

Infrared laser radiation in the range of 10.4 or 9.4 micrometers is provided by a Coherent Radiation Laboratories model 41 continous-wave CO₂ laser. The exact laser frequencies are verified using an Optical Engineering CO₂ spectrum analyzer. In single line operation, output powers between 10 and 150 W/cm² are obtained by variation of the CO₂ -N₂ -He gas mixture in the laser. The beam size is measured from burn patterns and is found to be approximately circular with a 4 mm diameter.

EXAMPLE 1

Dimethylsulfide is admitted to the reaction cell and decomposed following irradiation at R(18) of (00°1-10°0) for 5 seconds at 100 watts/centimeters square (100 W/cm²). The products formed are methane, ethene, and sulfur.

EXAMPLE 2

A mixture of the dialkylsulfide, (CH₃)₂ S, and the dialkylcadmium, (CH₃)₂ Cd in the reaction cell is irradiated at R(18) of (00°1-10°0), 979 cm⁻¹ for a total of 5 seconds at 100 W/cm². CdS is formed on the window and methane and ethane remains in the gaseous mixture.

Sulfur hexafluoride is mixed with (CH₃)₂ S and (CH₃)₂ Cd in the reaction cell as an intensifier. SF₆ has a fundamental at 944 cm⁻¹ which allows the excitation to occur by absorption of energy followed by collisional transfer to other molecules. Excitation occurred using P(20) of (00°1-10°0) at 944 cm⁻¹ for 5 seconds at 100 W/cm². The result of using SF₆ is the enhanced reaction of the excited elements of said (CH₃)₂ S and (CH₃)₂ Cd to produce CdS in larger quantities.

Table I below identifies the frequencies used to identify the products depicted by the infrared spectra curves A, B, and C of FIG. 2.

                  TABLE I                                                          ______________________________________                                         VIBRATIONAL FREQUENCIES (cm.sup.-1).sup.(a) of (CH.sub.3).sub.2 Cd,            (CH.sub.3).sub.2 S and REACTION PRODUCTS                                               (CH.sub.3).sub.2 Cd +                                                                     Mixture After       Refer-                                  (CH.sub.3).sub.2 Cd                                                                    (CH.sub.3).sub.2 S                                                                        Irradiation                                                                               Identity ence                                    ______________________________________                                                            3016       CH.sub.4 (c)                                     2900    2990       2990       X,Y(b)   (d)(e)                                  2980    2980       2980       X,Y                                              2973    2973       2973       X,Y                                              2925    2925       2925       X,Y                                              2918    2918       2918       X,Y                                                      2868       2870       X,Y                                              2855    2855       2855       X,Y                                                      2838                                                                   2349    2349       2349       X,Y                                                      1457                                                                           1441                                                                           1433                                                                   1338    1338       1338       X,Y,                                             1326    1326       1326       X,Y                                              1314    1314       1314       X,Y                                              1305    1305       1302       X,Y                                              1165    1045       1045       X,Y                                                      1025       1021       X,Y                                                                  948       Ethylene (c)                                              730        730                                                                 704        704                                                                 691        691                                                                 669        669                                                         544     544        544                                                         524     524        524                                                        ______________________________________                                          .sup.(a) Only the frequencies of major bands are given                         (b) X = (CH.sub.3).sub.2 Cd; Y = (CH.sub.3 ).sub.2 S                           (c) Herzberg, G., Infrared and Raman Spectra (Van Nostrand Reinhold, New       York, 1945), First Edition.                                                    (d) Bakhe, A. M. W., J. Mol. Spectrosc. 41, 1-19 (1972).                       (e) P. Groner, J. F. Sullivan, and J. R. Durig, in Vibrational Spectra an      Structures, edited by J. R. Durig (Elsevier, Amsterdam, 1986), Vol. 9,         Chap. 6.                                                                 

Table II below identifies the vibrational frequencies (cm⁻¹) used to identify the reactants and reaction products of (CH₃)₂ S, (CH₃)₂ Cd, and SF₆.

                  TABLE II                                                         ______________________________________                                         VIBRATIONAL FREQUENCIES (cm.sup.-1).sup.(a) of (CH.sub.3).sub.2 S,             (CH.sub.3).sub.2 Cd and SF.sub.6 and REACTION PRODUCTS.                                   Mixture +  After            Refer-                                  (CH.sub.3).sub.2 Cd + SF.sub.6                                                            (CH.sub.3).sub.2 S                                                                        Irradiation                                                                              Identity                                                                              ence                                    ______________________________________                                                               3016 (.9) CH.sub.4                                                                              (e)                                     2990                  2988 (.2) X,Y(b) (d),(c)                                 2980                  2979 (.2) X,Y                                            2970       2970       2969 (.2) X,Y                                                                  2958 (.2)                                                2951       2945       2948 (.2)                                                           2940       2938 (.2)                                                           2930       2927 (.2)                                                           2916       2917 (.2)                                                           2864                                                                           2851                                                                           2840                                                                1558       1558       1558 (.5)                                                1541       1541       1541 (2.9)                                                                     1532 (.4)                                                1521                  1523 (1.3)                                               1507       1507       1508 (.6)                                                                      1489 (.2)                                                                      1473 (.2)                                                1457       1457       1457 (.2) X,Y    (d),(c)                                            1437                                                                           1430                                                                                      1362      X,Y    (d),(c)                                            1339       1340                                                                1314                                                                           1304       1304                                                     945.6       945        945      SF.sub.6                                                                              (c)                                                 930        930                                                      724                   729                                                                            711                                                      705        704                                                                 692        691                                                                 669         669                                                                626        626        629                                                      614        615        614                                                      603        603        603                                                      544        544                                                                 527        527                                                                ______________________________________                                          .sup.(a) Only the frequencies of a major bands are given.                      (b) X = (CH.sub.3).sub.2 Cd; Y = (CH.sub.3).sub.2 S                            (c) Herzberg, G., Infrared and Raman Spectra (Van Nostrand Reinhold, New       York, 1945), First Edition.                                                    (d) Bakhe, A. M. W. J. Mol. Spectrosc. 41, 1-19 (1972).                        (e) P. Groner, J. F. Sullivan, and J. R. Durig, in Vibrational Spectra an      Structures, edited by J. R. Durig (Elsevier, Amsterdam, 1986), Vol. 9,         Chap. 6.                                                                  

I claim:
 1. A method for the synthesis of cadmium sulfide by the laser-induced chemical reaction between a first reactant selected from a dialkylcadmium compound and a second reactant selected from a dialkylsulfide compound, said method comprising:(i) providing a stainless steel reaction cell adapted for use with vacuum line techniques and equipped with O-ring seals for securing ZrSe windows onto said reaction cell for transmitting laser radiation and for securing potassium chloride windows onto said reaction cell to achieve monitoring of said laser-induced chemical reaction including the reaction products formed; (ii) metering said first reactant of said dialkylcadmium compound and said second reactant of said dialkylsulfide into said reaction cell to form a reaction mixture of said dialkycadmium compound in the range from about 14 to about 32 torr and of said dialkylsulfide compound in the range from about 30 to about 279 torr; (iii) irradiating said reaction mixture with infrared laser radiation in the range of 10.4 or 9.4 micrometers as provided by a continuous-wave CO₂ laser operating in a predetermined single line operation with an output power between about 10 and 150 watts per centimeter square (W/cm²) to form reaction products including a solid compound; and, (iv) recovering said solid compound which is high purity thermodynamically stable cadmium sulfide.
 2. The method of claim 1 wherein said dialkylcadmium is dimethylsulfide and wherein said reaction mixture comprises said dimethylcadmium of about 3 torr and said dimethylsulfide of about 100 torr.
 3. The method of claim 1 wherein said irradiating of said reaction mixture is achieved with said predetermined single line operation at R(18) of (00°1-10°0) for about 5 seconds at 975 cm⁻¹, said output power is 100 W/cm², and wherein said dialkylcadmium compound is dimethylcadmium of about 33 torr and said dialkylsulfide compound is dimethylsulfide of about 100 torr which comprises said first and second reactant respectively of said reaction mixture.
 4. The method of claim 1 wherein said reaction mixture additionally comprises SF₆ as an intensifier which has a fundamental at 944 cm⁻¹ to allow excitation to occur by absorption of energy followed by collisional transfer to said first reactant and to said second reactant to achieve enchanced reaction of the excited elements of said first and said reactants to produce said cadmium sulfide in higher yield.
 5. The method of claim 4 wherein said reaction mixture comprises said SF₆ of about 6 torr, said first reactant of said dialkylcadmium is dimethylcadmium of about 22.4 torr, said second reactant of said dialkylsulfide is dimethylsulfide of about 54.5 torr, and wherein said irradiation of said reaction mixture is achieved with said predetermined single line operation at P(20) of (00°1-10°0) for about 5 seconds at said output power which is 100 W/cm². 